Ceramic/polymer matrix for electrode protection in electrochemical cells, including rechargeable lithium batteries

ABSTRACT

Articles and methods for forming ceramic/polymer composite structures for electrode protection in electrochemical cells, including rechargeable lithium batteries, are presented.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/842,936, filed Jul. 3, 2013, which is incorporated herein byreference in its entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with government support under Grant No.DE-AR0000067 awarded by the Department of Energy ARPA-E program (ARPA-EBEEST DE-FOA-00000207-1536). The government has certain rights in theinvention.

FIELD

Articles and methods for forming composite structures for protection ofelectrodes in electrochemical cells, including rechargeable lithiumbatteries, are provided.

BACKGROUND

There has been considerable interest in recent years in developing highenergy density batteries with lithium containing anodes. Lithium metalis particularly attractive as the anode of electrochemical cells becauseof its extremely light weight and high energy density, compared forexample to anodes, such as lithium intercalated carbon anodes, where thepresence of non-electroactive materials increases weight and volume ofthe anode, and thereby reduces the energy density of the cells, and toother electrochemical systems with, for example, nickel or cadmiumelectrodes. Lithium metal anodes, or those comprising mainly lithiummetal, provide an opportunity to construct cells which are lighter inweight, and which have a higher energy density than cells such aslithium-ion, nickel metal hydride or nickel-cadmium cells. Thesefeatures are highly desirable for batteries for portable electronicdevices such as cellular phones and laptop computers where a premium ispaid for low weight. Unfortunately, the reactivity of lithium and theassociated cycle life, dendrite formation, electrolyte compatibility,fabrication and safety problems have hindered the commercialization oflithium cells.

Although there have been developments in protected lithium anodes,improvements are needed.

SUMMARY

Articles and methods for forming composite structures for protection ofelectrodes in electrochemical cells, including rechargeable lithiumbatteries, are provided. The subject matter herein involves, in somecases, interrelated products, alternative solutions to a particularproblem, and/or a plurality of different uses of one or more systemsand/or articles.

In one aspect, an electrode for an electrochemical cell is provided. Theelectrode comprises a base layer comprising an active electrode species,and a protective structure positioned to protect the electrode from anelectrolyte when the electrode is arranged in an electrochemical cell,the protective structure having a first side facing the active electrodespecies, and a second side arranged to face an electrolyte. Theprotective structure comprises at least a first and second compositelayer, each layer comprising a polymer matrix having a plurality ofcavities, and a ceramic material filling at least two cavities. Eachceramic-filled cavity is in ionic communication with the base layer. Theprotective structure has an average ionic conductivity of at least 10⁻⁷S/cm.

In another embodiment, an electrode for an electrochemical cellcomprises a base layer comprising an active electrode species, and aprotective structure including at least a first composite layercomprising a patterned array of cavities within a matrix, wherein apolymer or a ceramic material forms the matrix, and the other of thepolymer or ceramic material fills at least a portion of the cavities.The protective structure has an average ionic conductivity of at least10⁻⁷ S/cm.

In another embodiment, an electrode comprises a base layer comprising anactive electrode species and a protective structure positioned toprotect the electrode from an electrolyte when the electrode is arrangedin an electrochemical cell, the protective structure having a first sidefacing the active electrode species, and a second side arranged to facean electrolyte, wherein the protective structure comprises at least afirst and second composite layer, each layer comprising a continuouspolymer matrix having a plurality of cavities and a ceramic materialfilling at least two cavities, wherein each ceramic-filled cavity is inionic communication with the base layer, wherein the protectivestructure has an average ionic conductivity of at least 10⁻⁷ S/cm.

In another aspect, an electrode for an electrochemical cell is providedthat comprises a base layer comprising an active electrode species and aprotective structure comprising a polymer and a ceramic material,wherein the protective structure has an average ionic conductivity of atleast 10⁻⁷ S/cm and/or a polymer content of at least 2% by weight.

In yet another aspect, a method of fabricating a protective structure onan electrode is provided. The method comprising forming a base layercomprising an active electrode species attached to a protectivestructure, wherein the protective structure is formed by positioning ona substrate at least one layer of a matrix comprising a polymer or aceramic material, the matrix comprising a patterned array of cavities,and filling at least a portion of the cavities with the other of apolymer or a ceramic material to form a composite layer. The compositelayer has an average ionic conductivity of at least 10⁻⁷ S/cm.

In another embodiment, a method comprises providing, on at least onesurface of the electrode, a base component comprising a continuouspolymer matrix having cavities, and impregnating the base component witha ceramic material such that the composite structure has an averageionic conductivity of at least 10⁻⁷ S/cm.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments will be described by way of example withreference to the accompanying figures, which are schematic and are notintended to be drawn to scale. In the figures, each identical or nearlyidentical component illustrated is typically represented by a singlenumeral. For purposes of clarity, not every component is labeled inevery figure, nor is every component of each embodiment of the inventionshown where illustration is not necessary to allow those of ordinaryskill in the art to understand the invention. In the figures:

FIG. 1 is a schematic illustration of a top view of a protectivestructure according to one set of embodiments;

FIG. 2 is an angled view of the protective structure shown in FIG. 1according to one set of embodiments;

FIG. 3 is an illustrative embodiment showing an article including aprotective structure having multiple layers according to one set ofembodiments;

FIG. 4 is an illustrative embodiment showing another article including aprotective structure having multiple layers according to one set ofembodiments;

FIG. 5 is an illustrative embodiment showing the deposition of aninorganic material filling regions between polymer portions according toone set of embodiments;

FIGS. 6A-6E show a process for forming a protective structure accordingto one set of embodiments;

FIGS. 7A and 7B show different methods for forming layers of aprotective structure according to one set of embodiments;

FIGS. 8A and 8B show patterns of ceramic islands on a substrateaccording to one set of embodiments;

FIG. 9A shows an image of the ceramic pattern of FIG. 8A;

FIG. 9B shows an EDS mapping of the ceramic pattern of FIG. 9A; and

FIGS. 10A and 10B show images of a ceramic-polymer composite structureaccording to one set of embodiments.

DETAILED DESCRIPTION

Articles and methods for forming composite structures for electrodeprotection in electrochemical cells, including rechargeable lithiumbatteries, are provided. Certain embodiments relate to an electrode witha protective structure that can inhibit passage of one or moreundesirable components of an electrolyte that can adversely affect theelectrode. Advantageously, in some embodiments, the protective structuremay also promote passage of one or more desirable electrolyte components(e.g., metal ions) and may have favorable mechanical characteristicsthat reduce the likelihood of structural and functional failure of theprotective structure. In some embodiments, the protective structure ispositioned to protect the electrode from an electrolyte when theelectrode is arranged in an electrochemical cell, the protectivestructure having a first side facing a base layer of the electrodecomprising an active electrode species and a second size arranged toface an electrolyte. The protective structure may, in certain cases,comprise at least a first and second composite layer, each layercomprising a polymer matrix having a plurality of cavities and aninorganic material filling at least two cavities, wherein each inorganicmaterial-filled cavity is in ionic communication with a base layercomprising an active electrode species. The cavities may be arranged ina pattern within a composite layer of the protective structure.

The composite structures described above and herein may provide a numberof advantages over prior electrode protective structures. For example,the plurality of inorganic material-filled cavities may provide aplurality of ionic pathways from one side of the protective structure tothe other (i.e., between the electrode and the electrolyte). Whilecertain ceramic/glassy cells or layers may include pinholes, cracks,and/or grain boundary defects that can propagate throughout the entirecell or layer, the presence of a plurality of ionic pathways canminimize the effects of a defect in any one ionic pathway. Accordingly,in the structures described herein, when defects exist, they aretypically significantly less detrimental than they would be in aprotective structure comprising one or more continuous ceramic layers.For instance, because the defects may be isolated (e.g., surrounded atleast partially by a polymeric material), propagation of the defects toother ionic pathways (e.g., inorganic material-filled cavities) can bereduced or avoided.

Another advantage of the composite protective structure as describedherein relates to the favorable mechanical properties of the structure.The positioning of inorganic material-filled cavities or cells within apolymer matrix can decrease the susceptibility of the inorganicmaterial-filled cavities to cracking failure mechanisms. The presence ofthe polymer matrix can provide flexibility and strength, allowing thecomposite structure to be more flexible, more robust and/or more easilyhandled than, for example, a continuous inorganic or ceramic layer.Advantageously, since there is a plurality of ionic pathways through theinorganic material, there is no requirement that the polymer beionically conductive. The polymer may be a non-ironically conductivepolymer. In other embodiments, however, and ionically-conductive polymermay be used.

Examples of protective structures are now described.

FIG. 1 shows an illustrative embodiment of a top view of a protectivestructure 5. As illustrated, the protective structure includes at leastone layer comprising a patterned array of cavities within a matrix,wherein a polymer or a ceramic material forms the matrix, and the otherof the polymer or ceramic material fills at least a portion of thecavities. In this illustrative embodiment, the protective structureincludes a 6×6 cell structure where inorganic material portions 10 mayinclude, for example, an ionically conductive inorganic material (e.g.,ceramic) having a dimension n on each side, which portions formfilled-cavities within a matrix. Polymeric portions 15 of the structurehave a dimension d, which form the matrix. As described in more detailbelow, the polymeric portions may be in the form of a non-conductivepolymer mesh, or a conductive polymer mesh.

FIG. 2 shows the same single layer protective structure 5 from a 30°viewing angle. Again, inorganic material portions 10 and polymericportions 15 are shown. The depth of the blocks of the inorganic materialportions would be variable, and can be adjusted, for example, via theinitial coating of the polymer matrix. The protective structure mayinclude a first side facing a base layer of the electrode comprising anactive electrode species and a second size arranged to face anelectrolyte. Additional layers may be positioned adjacent or on top ofsuch a protective structure 5 as described in more detail below.

As used herein, when a layer is referred to as being “on”, “on top of”,or “adjacent” another layer, it can be directly on, on top of, oradjacent the layer, or an intervening layer may also be present. A layerthat is “directly on”, “directly adjacent” or “in contact with” anotherlayer means that no intervening layer is present. Likewise, a layer thatis positioned “between” two layers may be directly between the twolayers such that no intervening layer is present, or an interveninglayer may be present.

FIG. 3 is an illustrative embodiment showing an article 16 including aprotective structure 17. Protective structure 17 includes multiplelayers 5A-5D of composite materials separated by layers of inorganicmaterial 20A-20D. In this illustrative embodiment, each layer ofcomposite material (e.g., layers 5A-5D) can include inorganic materialportions 10A-10D separated by polymeric portions 15A-15D.

As illustrated, the protective structure includes at least one layer(e.g., a first composite layer) comprising a patterned array of cavitieswithin a matrix, wherein a polymer or a ceramic material forms thematrix, and the other of the polymer or ceramic material fills at leasta portion (or all) of the cavities. A second composite layer may beformed by positioning on the first layer (or on an intervening layer), asecond layer of a matrix comprising a polymer or a ceramic material, thesecond layer of matrix comprising a patterned array of cavities, andfilling at least a portion of the cavities of the second layer with theother of a polymer or a ceramic material to form a second compositelayer.

The material used to form the inorganic material portions of each layer(e.g., portions 10A-10D) may be the same or different. Similarly, thematerial used to form the polymeric portions of each layer (e.g.,portions 15A-15D) may be the same or different. Between each layer 5A-5Dmay be positioned (e.g., adjacent or on top of a composite layer), aninorganic material layer (e.g., layers 20A-20 D) which may be the sameas or different from an inorganic material used to form inorganicmaterial portions 10A-10D. Inorganic material layers 20A-20D may be, insome embodiments, a continuous inorganic material layer, i.e., it maysubstantially traverse across the width and/or length of the protectivestructure without substantial discontinuities (e.g., gaps, holes, pores)in the layer. In certain embodiments, inorganic material layers 20A-20Dmay be conductive to ions (e.g., lithium ions) of the electroactivematerial used in the corresponding electrode.

As shown in the embodiment illustrated in FIG. 3, protective structure17 may include polymeric portions 15 that are at least partially, or insome embodiments substantially or completely, surrounded by inorganicmaterial portions 10, as well as inorganic material portions 10 that areat least partially, or in some embodiments substantially or completely,surrounded by polymeric portions 15. Together, the composite structuremay be substantially impervious to components that adversely affect theelectroactive layer, thereby protecting the electroactive layer fromsuch components (e.g., species in an electrolyte solvent, or theelectrolyte solvent itself). Additionally, each layer 5A-5D may besubstantially impervious to such components. That is, each layer 5A-5D,as well as intervening layers 20A-20D, may be designed to have anabsence of cavities, gaps, holes, pores, or other areas in which adversecomponents can reside (other than defects such as cracks that may resultfrom handling and/or use of the protective structure). For instance,each layer may be substantially nonporous. Thus, a substantially filledsolid (e.g., nonporous) protective structure may be fabricated. Itshould be appreciated though that in other embodiments, not all cavitiesneed be filled with a solid material (e.g., a polymeric material or aninorganic material as described herein) as long as the protectivestructure as a whole is substantially impervious.

Also shown illustratively in FIG. 3, article 16 also includes asubstrate 30 on surface 32 of which protective structure 17 ispositioned. In certain embodiments, the substrate may be a polymer gellayer. In some such embodiments, and electroactive layer may bepositioned on a side opposite the polymer gel layer, e.g., againstsurface 35 of the protective structure. In other embodiments, substrate30 may be an electroactive layer as described herein. For example,substrate 30 may be a lithium metal layer, which may optionally bepositioned on a substrate as described herein. In yet other embodiments,substrate 30 may be another protective structure or layer (e.g., aninorganic material layer or polymer layer), which may be substantiallyimpervious to a liquid electrolyte to be used with the cell in which theprotective structure is incorporated. In other instances, substrate 30is a carrier substrate that is removed prior to inserting the protectivestructure into an electrochemical cell. In some such embodiments, thelayer or surface directly adjacent substrate 30 may have a relativelylow adhesive affinity to substrate 30 so as to facilitate release of theprotective structure from the substrate. An intervening release layermay be present between the protective structure and the substrate insome embodiments. Other configurations are also possible. The protectivestructure may include a first side facing a base layer of the electrodecomprising an active electrode species and a second size arranged toface an electrolyte.

FIGS. 1-3 indicate the form of the inorganic material (e.g., ceramic)and polymer elements that may be possible in certain embodiments ofprotective structures described herein. Such structures, the inherentstrengths of the polymer and inorganic materials (e.g., ceramicmaterials) may be accentuated while their weaknesses may be minimized.Unlike certain previously-described flat sheet protected electrodeswhere one individual layer, be it either inorganic material (e.g.,ceramic) or polymer, is built upon the previous layer, the protectivestructures described herein may include at least one layer having amaterial embedded in another to form a composite structure.

The starting point for the protective structures described herein may bea polymer matrix, such as a non-ionically conductive and/ornon-electronically conductive polymer matrix, although conductivepolymer matrices (e.g., ionically conductive polymer matrices) can alsobe used. An ordered structure, such as a square grid arrangement isshown for explanatory purposes, but other ordered matrices, such as ahoney-comb or diamond pattern, may be used as well. In otherembodiments, disordered structures/arrangements may be used. In someembodiments, the walls of the polymer structure are set to apredetermined thickness, while the hollow central portions of the gridare filled with an inorganic material (e.g., an ionically conductiveinorganic material such as a ceramic). Examples of such materialsinclude Li₂O, Li₃N, sulfide glass, or another suitable ionic conductor,as well as those described in more detail below.

It should be appreciated that in other embodiments, the starting pointmay be an inorganic material/ceramic matrix. In some embodiments, thewalls of the inorganic material/ceramic matrix are set to apredetermined thickness, and then the cavities between the inorganicmaterial/ceramic portions are filled with a polymeric material.

By examining FIGS. 1-3, one can see that ionic paths exist from the topof the structure to the bottom of the structure through a series ofcolumns. For instance, as shown illustratively in FIG. 3, since a flatsheet or layer 20A-20D of inorganic material (e.g., ionically conductiveinorganic material such as a ceramic) is positioned at the top of eachcomposite layer 5A-5D, and forms the base of the next layer, all theinorganic material (e.g., ceramic) columns 40 are interconnected,resulting in numerous ionic paths from top to bottom (e.g., from surface35 to 32) and vice-versa. This in turn implies that if a defect of crackexists in any column, or in any portion of one of the inter-connectinginorganic material (e.g., ceramic) layers or sheets, that numerous otherconductive paths still exist to allow for ion transfer. Unlike the casein the certain existing protective structures comprising alternatinglayers of ceramic and polymer, where a single crack or defect in aceramic layer may compromise the function of that layer (e.g., byallowing the crack or defect to propagate across the layer), in theprotective structures described herein, the loss of a few segments dueto cracks or defects will not seriously compromise that layer becausenumerous other current paths exists for ions looking to move to the nextlayer.

This approach is similar to that used with segmented film capacitors,where the total capacitance is the sum of smaller capacitors connectedin parallel. If one segment is lost there is little effect on theoverall function of the aggregate capacitor. Additionally, unlikecertain existing protective structures, the protective structuresdescribed herein do not necessarily require an ionically conductivepolymer layer (e.g., an ionically conductive polymer), and hence, insuch embodiments, is not troubled by the low conductivity problems andswellability issues that may be associated with some of these materials.Instead, a non-ionically conductive polymer can be employed in someembodiments, allowing for a larger number of choices, and increasedflexibility for the inorganic material (e.g., ceramic) columns encasedwithin each layer. As described herein, however, ionically conductivepolymer materials can be used in place of, or in addition to,non-ionically conductive polymer materials in some embodiments.

Mechanically, the protective structures described herein may offer anumber of benefits over certain existing protective structures. Forinstance, instead of discrete inorganic material (e.g., ceramic) layersmade up of large flat sheets (separated by intervening polymer layersalso in the form of flat sheets), which are susceptible to mechanicaldamage either through handling or flexing under lithium plating andstripping operations, the smaller sections of inorganic material (e.g.,ceramic) may be cushioned via a surrounding polymer network. In otherwords, the presence of embedded polymeric material portions betweensections of inorganic material portions can limit the propagation of anycracks are defects in the inorganic material portions, thereby isolatingsuch cracks are defects to certain regions of the inorganic material.The situation is akin to how large glass telescope mirrors areconstructed; smaller sections of glass connected together by a honeycombsupport network, instead of one large sheet of glass which is prone tocracking when subject to flexing.

In another embodiment of a protective structure described herein, thepolymer matrix is purposely graded such that more and/or smallerinorganic material (e.g., ceramic) segments (e.g., inorganic materialportions having a relatively smaller cross-sectional dimension) arelocated towards the edges of the structure/composite layer (e.g., theleft and right-hand sides of the structures shown in FIGS. 1 and 3),compared to those portions located towards the center of the structure.In such embodiments, a gradient in the size of inorganic materialportions may be present across at least a portion of the width of thestructure/composite layer. Such an arrangement may lead to a higherpolymer density and/or higher volume of polymer at the edges compared tothe center of the structure/composite layer, but this in turn gives thestructure more flexibility at the edges where the sheer forces areexpected to be the greatest during plating and stripping operations.

It should be pointed out that the sum of the surface areas presented bythe portions of inorganic material (e.g., columns) at surface 32, i.e.,at an interface between the protective structure and substrate 30 inFIG. 3 (e.g., a gel-column interface), βn², where β is the total numberof inorganic material portions (e.g., columns) in contact with thesubstrate, will approach the surface area of a flat inorganic material(e.g., ceramic) sheet as the number of inorganic materialportions/columns is increased. Hence, basic functionality is preservedwhile mitigating basic flat sheet failure issues.

In some embodiments, the average width (or cross-sectional dimension) ofthe inorganic material portions of a composite layer of a protectivestructure is at least 1 time, at least 1.2 times, at least 1.5 times, atleast 2 times, at least 3 times, at least 5 times, at least 7 times, atleast 10 times, at least 15 times, at least 20 times, at least 30 times,at least 40 times, at least 50 times, at least 75 time, or at least 100times the average width (or cross-sectional dimension) of the polymericportions of the same layer. In certain embodiments, the average width(or cross-sectional dimension) of the inorganic material portions of thecomposition layer may be less than or equal to 200 times, less than orequal to 150 times, less than or equal to 100 times, less than or equalto 80 times, less than or equal to 50 times, less than or equal to 30times, less than or equal to 20 times, or less than or equal to 10 timesthe average width (or cross-sectional dimension) of the polymericportions of the same layer. Combinations of the above referenced rangesare also possible.

Just as importantly, the articles and methods described herein may allowfor scalability. Consider the construction and handling issuesassociated with constructing a 1M×1M inorganic material (e.g., ceramic)sheet. The error margin involved in such operations is greatly reducedover making 2M×2M sheets; to the point that serious questions arise asto the feasibility of such an approach. With the articles and methodsdescribed herein, these conditions are greatly relaxed, given that thesmaller sizes of inorganic material portions (e.g., columns) may be theprimary point of concern. The flat inter-connecting sheets/layers ofinorganic material (e.g., layers 20A-20D), if present, are free to havecracks and defects in them given the total number of inorganic materialportions (e.g., columns) available for conduction.

In another embodiment of the above approach, the flat inter-connectingsheets/layers of inorganic material (e.g., layers 20A-20D) may beremoved from the protective structure. Although doing so may lead to amore difficult realization of the protective structure in terms ofconstruction, it has mechanical benefits. An example of such a structureis shown in FIG. 4. Note that in this case the polymer portions shouldbe registered correctly as the layers are built one upon another. Inthis instance the columns may end up being staggered during constructionsuch that the layer above the first one is re-centered to make contactwith the columns below it (hence creating the different possibleconduction paths). As shown illustratively in FIG. 4, multiple columns40 of inorganic material may be present in the protective structure.

As described herein, the disclosed protective structures may correctsome layer by layer limitations encountered with certain existinglayered protective structure configurations by accentuating thestrengths of the materials involved: flexibility, multiple ionic pathsfor the inorganic material (e.g., ceramic) to handle cracks and defects,and in some instances, no need for ion conduction within the polymer.The enhanced flexibility of this structure should also prove beneficialin terms of handling properties, especially if de-lamination from asubstrate is still required or desired.

The structures described herein also have numerous applications outsideof the battery field. The ability to make a flexible inorganic material(e.g., ceramic) structures leads to military applications in terms of IRdeception and radar deception with the correct selection of materials.The flexibility component of the proposed structure in turn, leads tothe possible inclusion of such a structure in tents, tarps, and evenclothing. It may well be possible to cover objects like unmanned aerialvehicles (UAVs) or ground droids with sections of this material, or itmay be possible to apply the materials to cover portions of largervehicles to enhance or reduce their radar/IR signature. It may even bepossible to make active, adaptive camouflage patterns. No doubt numerousother potential applications exist as well.

There are multiple paths to the physical realization of the aboveapproach, examples of which are described in more detail below.

Generally, methods described herein may involve forming a base layercomprising an active electrode species attached to a protectivestructure. The protective structure may be formed by positioning on asubstrate at least one layer of a matrix comprising a polymer or aceramic material, the matrix comprising a patterned array of cavities,and filling at least a portion of the cavities with the other of apolymer or a ceramic material to form a composite layer. The compositelayer may have an average ionic conductivity of at least 10⁻⁷ S/cm.

In such embodiments, the substrate may be the base layer (e.g., lithiummetal), i.e., the protective structure may be formed on theelectroactive layer. In other embodiments, the substrate may be acarrier substrate. In such embodiments, a base layer comprising anactive electrode species may be formed on top of the protectivestructure. Other substrates are also possible as described herein.

In some embodiments, a second composite layer may be formed on the atleast one layer of matrix, or on an intervening layer. The secondcomposite layer may include a second layer of a matrix comprising apolymer or a ceramic material, the second layer of matrix comprising apatterned array of cavities, and filling at least a portion of thecavities of the second layer with the other of a polymer or a ceramicmaterial to form the second composite layer. In such embodiments, thesecond layer may be positioned direction on the first composite layer,or an intervening layer such as a continuous ceramic material layer maybe positioned between the first and second composite layers.

The first element to consider are the polymeric portions (i.e., polymermatrix). There are several ways to deposit this matrix. The first wouldbe to deposit (e.g., flash deposit, coat, or apply in any other suitablemanner) a layer of polymer of the desired thickness. This material maythen be passed in front of a screen or mask. A polymer processingstation (e.g., a curing, drying, or crosslinking station such as a UVlamp, oven, or other suitable apparatus) may be located behind thisscreen/mask allowing for the curing, drying and/or crosslinking of justthe desired polymer pattern. The remaining uncured/undried/uncrosslinkedpolymer material, after passing by the mask and polymer processingstation, can be removed. For example, any uncured material may evaporatein the vacuum environment, a process that can be accelerated by the useof heat lamps. Another approach to the construction of the polymermatrix involves a printing technique. Any suitable printing techniquemay use; for example, a print roller where a viscous polymeric materialis transferred through a gravure roller either using a liquid reservoiror via injection into the roller through a pump. In this case thepattern is laid directly on the chosen substrate andcured/dried/crosslinked at a polymer processing station (e.g., viae-beam, UV, thermal, or chemical methods). Another option is to directlyprint the polymer matrix through more conventional ink-jet or nozzletype arrangements with curing, drying and/or crosslinking taking placeusing one of the previously described, or other suitable forms. Thislast method may be better suited to atmospheric situations.

The second element to consider is inorganic material (e.g., ceramic)deposition. These methods are well understood and include, for example,e-beam evaporation, sputtering, and thermal evaporation, among others.An issue arises at this step in terms of the actual inorganic material(e.g., ceramic) coating and the polymer matrix. This issue is shownillustratively in FIG. 5.

As shown in the embodiment illustrated in FIG. 5, areas where polymerportions 15 are not present (e.g., hollow portions of the polymermatrix) may be filled with an inorganic material (e.g., ceramic) 60.During filling, a “flat” interconnecting plate 65 may be created asdesired in one embodiment of the structure, but questions arise as tothe peaks 68 formed by the inorganic material (e.g., ceramic) coatingover the polymer walls after a few layers.

It is not clear that these peaks will pose a major issue given that arole of the polymer matrix is simply to add flexibility to the inorganicmaterial (e.g., ceramic). Under these circumstances the desiredinorganic material (e.g., ceramic) paths will still exist, and thesupporting polymer structure will still perform its required role.Should it be desired, methods may be employed to deal with the surfacevariations arising from the inorganic material (e.g., ceramic) coatingover the polymer matrix.

One approach may be to use a coating system or oil system, e.g., via asynchronized mask or a contact roller, to place a thin coating of oil orliquid over the raised portions of the cured, dried or crosslinkedpolymer mask. This sequence of events is shown in FIG. 6. As shownillustratively in FIGS. 6A-6E, polymeric portions 15A may be depositedin a desired pattern (FIG. 6A). A thin coating 70 of oil, liquid, or anyother suitable material for inhibiting adhesion of the inorganicmaterial to the polymeric material, may be placed over the polymericportions (FIG. 6B). Inorganic material (e.g., ceramic) 60 will notdeposit to this coating, and instead may be deposited in between thepolymeric portions to form inorganic material portions 10A (FIG. 6C).Coatings 70 may then be removed, e.g., via a light plasma treatment, asshown in FIG. 6D. Plasma treatment may be performed in the presence ofvarious gases such as: air, oxygen, ozone, carbon dioxide, carbonylsulfide, sulfur dioxide, nitrous oxide, nitric oxide, nitrogen dioxide,nitrogen, ammonia, hydrogen, freons (e.g., CF4, CF2Cl2, CF₃Cl), silanes(e.g., SiH₄, SiH₂(CH₃)₂, SiH₃CH₃), and/or argon. This same plasmatreatment may also have the beneficial effect of promoting adhesionbetween inorganic material (e.g., ceramic) layers, such as adhesionbetween the top surfaces of inorganic material portions 10A withsubsequent inorganic material portions to be deposited on top (notshown). Additional polymeric portions 15B may then be deposited in adesired pattern on top of inorganic material portions 10A (FIG. 6E).This process can be repeated until the desired number of compositelayers is fabricated.

Two possible systems for fabricating the structures described in FIG. 6,and the equipment required to implement these methods in a vacuumenvironment, are shown illustratively in FIGS. 7A and 7B.

In FIG. 7A, the approach involves use of a rotating drum 100. A sheet ofpolymer may be laid down via a polymer deposition process (e.g., flashdeposition process). The desired pattern in this sheet is obtained byusing a polymer processing unit 105 (e.g., a curing station that wouldUV-cure the polymer) through a physical mask 110. The uncured polymer,which is the central areas of the pattern, is then driven off by a heatlamp 115. It should be pointed out that this uncured polymer wouldeventually evaporate in the vacuum environment, but to accelerate thisprocess a heat lamp may optionally be employed. In other embodiments,the polymer can be dried and/or crosslinked in addition to oralternatively to being cured at the polymer processing unit. The nextstep involves a coating of oil, liquid, or other anti-adhesion materialmask. A mask applicator 120, such as a roller, be it patterned or not,is responsible for coating the top portions of the cured, dried and/orcrosslinked polymer pattern with this material so that inorganicmaterial (e.g., ceramic) will not deposit in these areas. The next stepan inorganic material deposition process 125 (e.g., an e-beam orsputtering system) which will deposit the inorganic material (e.g.,ceramic) into the hollow portions of the pattern. Lastly, a plasmatreatment 130 may be employed to remove the oil/liquid/anti-adhesionmaterial mask and increase the surface energy of the current inorganicmaterial (e.g., ceramic) layer in anticipation of the nextpolymer/inorganic material (e.g., ceramic) layer.

FIG. 7B is a variation on the previous scheme. In this embodiment aprinting unit 150 is used to print the polymer pattern is onto asubstrate and cured, dried and/or crosslinked using polymer processingunit 105. This approach dispenses with the heat lamp to drive off theundesired portions of the polymer coating. The rest of the system is asdescribed previously.

In embodiments in which an inorganic material/ceramic matrix isdeposited first, a masking system can be used to include a coating onthe inorganic material/ceramic portions so that the cavities between theinorganic material/ceramic portions are filled with a polymericmaterial, but the polymeric material does not adhere to the inorganicmaterial/ceramic portions.

Another fabrication process involves printing the inorganic material(e.g., ceramic)/polymer portion of the composite structure. Consider athree dimensional polymer matrix printed via screen printing or maskingapproaches outside of a vacuum environment. The hollow portions of sucha matrix could then be filled with inorganic material (e.g., ceramic)powders, or an inorganic material (e.g., ceramic) slurry, and if thepolymer material is chosen correctly for temperature, then fired tosinter the contained inorganic materials (e.g., ceramics). Inorganicmaterials such as halides and oxy-sulfides (e.g., lithium oxy-sulfides)may be good choices for this approach as both require low temperaturesfor sintering. One issue to consider in such an effort is the thicknessof the inorganic material (e.g., ceramic) layers deposited. In someembodiments, a reduction in powder grain size may be required. Even so,this method of manufacturing, which may involve vacuum deposition foronly the final lithium deposition step, may offer major economicadvantages over the all vacuum approach.

It should be appreciated that while FIGS. 1-6 show variousconfigurations of protected structures, in some embodiments not allcomponents shown in the figure need be present. It should also beappreciated that other components that are not shown in the figures maybe included in the protective structures in some embodiments. Forexample, in place of or in addition to inorganic material layers20A-20D, one or more ion-conductive polymer layers may be present insome embodiments. Additionally, other components not shown in thefigures may be present in certain articles described herein (e.g., anelectroactive layer may be positioned on one side of the protectivestructure in addition to a polymer gel layer positioned on the otherside of the protective structure). Other configurations are alsopossible.

In a specific embodiment of the invention, a protected electrode may bean anode in a lithium battery. Lithium battery systems generally includea cathode which is electrochemically lithiated during the discharge. Inthis process, lithium metal is converted to lithium ion and transportedthrough the electrolyte to the battery's cathode, where it is reduced.In a lithium/sulfur battery, for example, lithium ion forms one of avariety of lithium sulfur compounds at the cathode. Upon charging, theprocess is reversed, and lithium metal is plated, from lithium ion inthe electrolyte, at the anode. In each discharge cycle, a significantamount (e.g., up to 100%) of available Li may be electrochemicallydissolved in the electrolyte, and nearly this amount can be re-plated atthe anode upon charge.

This process can be stressful to the electrode in many ways, and it canlead to premature depletion of Li and reduction of the battery cyclelife. One means of protecting an electrode is by having a ceramic layerthat serves as an electronic insulator, acting as an electrolytebarrier. In certain prior art structures, the ceramic layers weresometimes treated with a polymer to fill in defects. However, suchtreatments could, in some instances, impede diffusion of certain speciestowards the electrode and reduce ionic conductivity.

As described herein, an electrode may include a protective structurethat can be used to prevent or inhibit reaction of an electroactivelayer with other components to be used with the electrode. Examples ofsuch reactive components include electrolytes (e.g., solvents and salts)and cathode discharge products. In some embodiments, the protectivestructure comprises at least a first and second composite layer, eachlayer comprising a polymer matrix having a plurality of cavities and aninorganic material filling at least two cavities. Each inorganicmaterial-filled cavity may be in ionic communication with the baselayer. Each inorganic material-filled cavity may be in ioniccommunication with both sides of the protective structure (i.e., thebase layer comprising an active electrode species and the electrolyte).Advantageously, the structure can provide a plurality of ionic pathwaysfrom one side of the protective structure to the other side. This is anadvantage because inorganic material such as ceramics may have defectsthat lead to crack nucleation and propagation. As the area of theceramic increases, the number of defects encountered increasesproportionally. If a continuous layer of ceramic material is used toprotect an electrode, a crack may lead to failure of the ceramic layer.If, however, a plurality of inorganic material-filled cavities arearranged in a polymer matrix and provide a plurality of ionic pathwaysfrom one side of the protective structure to the other, the effect of adefect in any one pathway is minimized. Additionally, the smallerinorganic material/ceramic cells cushioned by a polymer matrix may beless susceptible to cracking during flexing than a continuous inorganicmaterial/ceramic layer.

In some embodiments, the average ionic conductivity of the protectivestructure is at least about 10⁻⁷ S/cm, at least about 10⁻⁶ S/cm, atleast about 10⁻⁵ S/cm, at least about 10⁻⁴ S/cm, at least about 10⁻²S/cm, at least about 10⁻¹ S/cm, at least about 1 S/cm, at least about10¹ S/cm, at least about 10² S/cm, at least about 10³ S/cm, at leastabout 10⁴ S/cm, or at least about 10⁵ S/cm. In some instance, theaverage ionic conductivity of the protective structure may be less thanor equal to about 10⁵ S/cm, less than or equal to about 10⁴ S/cm, lessthan or equal to about 10³ S/cm, less than or equal to about 10² S/cm,or less than or equal to about 10¹ S/cm. Combinations of the abovereferenced ranges are also possible.

The average ionic conductivity of the protective structures describedherein may be, in some embodiments, higher than the average ionicconductivity of protective structures in the prior art. For example, incertain embodiments in which a non-ionically conductive polymer is usedin the protective structure, the ions are not required to pass throughthe polymer to reach the electrode (or electrolyte). The ions passthrough the ionically conductive inorganic material (e.g., ceramic)portions, which may generally have a higher ion conductivity than anyionically conductive polymer portions that may be used. This feature, inwhich inorganic material-filled cavities provide a plurality of ionicpathways from one side of the protective structure to the other and ionsare not required to travel through a polymer, allows the protectivestructure to gain mechanical advantages from the presence of the polymerwithout suffering disadvantages relating to reduced ion conductivity.

In some embodiments, the protective structure comprises at least a firstand second composite layer. Any suitable number of compasses layers canbe included in the protective structure. For example, in someembodiments, the protective structure further comprises at least a thirdcomposite layer, at least a fourth composite layer, at least a fifthcomposite layer, at least a sixth composite layer, at least a seventhcomposite layer, at least an eighth composite layer, at least a ninthcomposite layer, or at least a tenth composite layer. Additional numbersof layers are also possible.

As described herein, a protective structure may include at least onelayer comprising a patterned array of cavities within a matrix, whereina polymer or a ceramic material forms the matrix, and the other of thepolymer or ceramic material fills at least a portion (or all) of thecavities. A patterned array of cavities may be distinguished from arandom arrangement of cavities by the presence of repeating units (e.g.,cavities distanced at predetermined, or regular intervals from oneanother).

The cavities of a matrix material such as polymer or an inorganicmaterial/ceramic (and the shapes of any material filling such cavities)may have any shape. As non-limiting examples, the cavities (and theshapes of any material filling such cavities) may have cross sectionsthat are substantially square, rectangular, pentagonal, hexagonal,octagonal, or circular. In some embodiments, all the cavities in a givencomposite layer may have the same shape. In other embodiments, at leastone cavity in a given composite layer has a different shape from atleast one cavity in the layer. In some cases, the cavities in acomposite layer in a protective structure may be the same size. In somecases, the cavities may be different sizes. Cavities may be filled orunfilled with material (e.g., inorganic materials such as ceramics,polymeric material) as described herein.

It should be appreciated that while in many embodiments inorganicmaterial-filled cavities are described with respect to a polymer matrix,in other embodiments a structure may include polymer-filled cavitieswith respect to an inorganic material/ceramic matrix. Thus, thedescription herein for cavities of a polymer matrix may apply tocavities of an inorganic material/ceramic.

In some embodiments, the average largest cross-sectional dimensions ofcavities (e.g., within a layer or within an entire protective structure)may be, for example, less than or equal to 10 microns, less than orequal to 5 microns, less than or equal to 2 microns, less than or equalto 1 micron, less than or equal to 500 nm, less than or equal to 300 nm,less than or equal to 100 nm, or less than or equal to 50 nm, less thanor equal to 10 nm. In some embodiments, the average largestcross-sectional dimensions of cavities may be greater than or equal to 5nm, greater than or equal to 10 nm, greater than or equal to 50 nm,greater than or equal to 100 nm, greater than or equal to 300 nm,greater than or equal to 500 nm, or greater than or equal to 1 micron.Other sizes are also possible. Combinations of the above-noted rangesare also possible (e.g., a largest cross-sectional dimension of lessthan 300 nm and greater than 100 nm). The average largestcross-sectional dimensions of the material (e.g., inorganic materialportions, or polymeric portions) that fill the cavities may also includevalues in the above referenced ranges.

In some cases, the maximum percentage difference between the largestcross-sectional dimensions of the cavities (e.g., in a layer, or in aprotective structure) may be less than 100%, less than 50%, less than20%, less than 10%, less than 5%, or less than 1%. In some instances,the maximum percentage difference between the largest cross-sectionaldimensions of the cavities (e.g., in a layer, or in a protectivestructure) may be at least 1%, at least 5%, at least 10%, at least 20%,at least 50%, at least 70%, or at least 100%. Combinations of the abovereferenced ranges are also possible. The maximum percentage differencebetween the largest cross-sectional dimensions of the material (e.g.,inorganic material portions, or polymeric portions) that fill thecavities (e.g., in a layer, or in a protective structure) may alsoinclude values in the above referenced ranges. In certain embodiments,the cavities near the edges of the layer or protective structure may besmaller than the cavities near the center of the layer or protectivestructure. Such an arrangement may provide more flexibility at the edgesof the structure, where shear forces may be greatest.

In some cases, each material (e.g., inorganic material, or polymericmaterial)-filled cavity in a composite layer may comprise the samematerial. In other cases, at least one material (e.g., inorganicmaterial, or polymeric material)-filled cavity in a composite layer maycomprise a different material than at least one other material-filledcavity in the same composite layer.

In some embodiments, a first composite layer in a protective structuremay have the same number of cavities as at least one other compositelayer in the protective structure. In some embodiments, the number ofcavities in a first composite layer in a protective structure may bedifferent from the number of cavities in at least one other compositelayer in the protective structure.

In certain cases, one or more cavities in a first composite layer in aprotective structure may be aligned with one or more cavities in atleast one other composite layer in the protective structure. Forinstance, a line drawn perpendicular to the horizontal plane of thecomposite layers may intersect a point on or within a cavity of a thefirst composite layer and a point on or within a cavity in a secondcomposite layer. Likewise, a material filling a cavity (e.g., aninorganic material/ceramic or a polymeric material) of a first compositelayer may be aligned with a material filling a cavity of a secondcomposite layer, e.g., such that a line drawn perpendicular to thehorizontal plane of the composite layers may intersect a point on orwithin the first material (e.g., an inorganic material/ceramic or apolymeric material) and a point on or within a second material (e.g., aninorganic material/ceramic or a polymeric material) in a secondcomposite layer. In certain embodiments, one or more cavities in a firstcomposite layer in a protective structure are not aligned with anycavity from at least one other composite layer in the protectivestructure.

In some cases, the cavities of different composite layers in aprotective structure may have different sizes, shapes, and/or locations.In some cases, the cavities of different composite layers in aprotective structure may have the same size, shape, and/or location. Incertain embodiments, inorganic material-filled cavities in differentcomposite layers in a protective structure may comprise differentinorganic materials. In certain embodiments, inorganic material-filledcavities in different composite layers in a protective structure maycomprise the same inorganic material. In some cases, the polymermatrices of different composite layers in a protective structure maycomprise different polymers. In some cases, the polymer matrices ofdifferent composite layers in a protective structure may comprise thesame polymer. The inorganic material (e.g., ceramic)-to-polymer massratio and/or volume ratio may be the same in different composite layersin a protective structure. The inorganic material (e.g.,ceramic)-to-polymer mass ratio and/or volume ratio may be different indifferent composite layers in a protective structure. In someembodiments, different composite layers in a protective structure mayhave different thicknesses. In some embodiments, different compositelayers in a protective structure may have the same thickness.

The thickness of a composite layer comprising polymer and inorganicmaterial may vary over a range from about 1 nm to about 10 microns. Forinstance, the thickness of a composite layer may be between 1-10 nmthick, between 10-100 nm thick, between 10-1000 nm thick, between100-1000 nm thick, between 1-5 microns thick, or between 5-10 micronsthick. The thickness of a composite layer may be no greater than, e.g.,10 microns thick, no greater than 5 microns thick, no greater than 1000nm thick, no greater than 500 nm thick, no greater than 250 nm thick, nogreater than 100 nm thick, no greater than 50 nm thick, no greater than25 nm thick, or no greater than 10 nm thick. In some embodiments, eachcomposite layer has a maximum thickness of less than 100 microns, lessthan 50 microns, less than 25 microns, less than 10 microns, less than 1micron, less than 100 nm, less than 10 nm, or less than 1 nm. In someembodiments, a composite layer is at least 1 nm thick, at least 10 nmthick, at least 20 nm thick, at least 30 nm thick, at least 50 nm thick,at least 100 nm thick, at least 400 nm thick, at least 1 micron thick,at least 2.5 microns thick, or at least 5 microns thick. Otherthicknesses are also possible. Combinations of the above-noted rangesare also possible. In certain embodiments, several composite layers,each having a thickness in one or more of the above-referenced ranges,are arranged in a protective structure.

In some embodiments, the thickness of the protective structure may varyfrom, e.g., about 2 to 200 microns. For instance, the protectivestructure may have a thickness of less than about 200 microns, less thanabout 100 microns, less than about 50 microns, less than about 25microns, less than about 10 microns, or less than about 5 microns. Theprotective structure may have a thickness of at least 1 micron, at least2 microns, at least 5 microns, at least 10 microns, at least 20 microns,or at least 50 microns. Combinations of the above referenced ranges arealso possible. The choice of the thickness may depend on cell designparameters such as cycle life. In one embodiment, the thickness of theprotective structure is in the range of about 2 to 100 microns. Inanother embodiment, the thickness of the protective structure is in therange of about 5 to 50 microns. In another embodiment, the thickness ofthe protective structure is in the range of about 5 to 25 microns. Inyet another embodiment, the thickness of the protective structure is inthe range of about 10 to 25 microns. In some particular embodiments, aprotective structure may have a thickness in one or more of theabove-referenced ranges for the thickness of a composite layer.

In some embodiments, the ratio of polymer to inorganic material (e.g.,ceramic) content in a composite layer (or a protective structure) may beat least 1%, at least about 5%, at least about 10%, at least about 20%,at least about 30%, or at least about 40% by volume.

In some embodiments, the volume of polymer in a composite layer (or aprotective structure) may be at least 1%, at least about 5%, at leastabout 10%, at least about 20%, at least about 30%, or at least about 40%of the total volume of material in the layer (or structure). The volumeof polymer in the composite layer (or a protective structure) may beless than or equal to about 60%, less than or equal to about 50%, lessthan or equal to about 40%, less than or equal to about 30%, less thanor equal to about 20%, or less than or equal to about 10% of the totalvolume of material in the layer (or structure). Combinations of theabove-referenced ranges are also possible.

In certain embodiments, the ratio of polymer to inorganic material(e.g., ceramic) content in a composite layer (or a protective structure)may be at least 1%, at least about 2%, at least about 5%, at least about10%, at least about 15%, at least about 20%, at least about 25%, or atleast about 30% by weight or mass.

In some embodiments, the mass/weight of polymer in a composite layer (ora protective structure) may be at least 1%, at least about 2%, at leastabout 5%, at least about 10%, at least about 15%, at least about 20%, atleast about 25%, at least about 30%, or at least about 40% of the totalmass/weight of material in the layer (or structure). The mass/weight ofpolymer in the composite layer (or a protective structure) may be lessthan or equal to about 60%, less than or equal to about 50%, less thanor equal to about 40%, less than or equal to about 30%, less than orequal to about 20%, or less than or equal to about 10% of the totalmass/weight of material in the layer (or structure). Combinations of theabove-referenced ranges are also possible.

In certain cases, the ratio of the sum of the surface areas of theinorganic material-filled (e.g., ceramic-filled) cavities (or inorganicmaterial/ceramic portions) to the surface area of the electrode may beat least about 0.2, at least about 0.3, at least about 0.4, at leastabout 0.5, at least about 0.6, at least about 0.7, at least about 0.8,at least about 0.9, or at least about 1. The ratio of the sum of thesurface areas of the inorganic material-filled (e.g., ceramic-filled)cavities (or inorganic material/ceramic portions) to the surface area ofthe electrode may be less than or equal to about 1, less than or equalto about 0.9, less than or equal to about 0.8, less than or equal toabout 0.7, less than or equal to about 0.6, less than or equal to about0.5, less than or equal to about 0.4, less than or equal to about 0.3,or less than or equal to about 0.2. Combinations of the above-referencedranges are also possible. The surface areas in the above-referencedranges may be, in some instances, the surface areas on an outer surfaceof the protective structure (e.g., the surface area exposed to anelectrolyte such as a liquid electrolyte).

Certain embodiments relate to methods of fabricating a protectivestructure including a polymer layer (which may be continuous ordiscontinuous). As described herein, in some embodiments, the polymerlayer includes regions of polymer that are interconnected with oneanother within the layer, while in other embodiments the regions areisolated from one another within the layer (e.g., an inorganicmaterial/ceramic may separate the polymeric regions from one another inthe layer). In some embodiments, a polymer layer may be deposited by amethod such as electron beam evaporation, vacuum thermal evaporation,laser ablation, chemical vapor deposition, thermal evaporation, plasmaassisted chemical vacuum deposition, laser enhanced chemical vapordeposition, jet vapor deposition, and extrusion. The polymer layer mayalso be deposited by spin-coating techniques. The technique used fordepositing the polymer layer may depend on the type of material beingdeposited, the thickness of the layer, etc.

In some embodiments, the deposited polymer layer may pass in front of ascreen or a mask. The screen or mask may be patterned. There may then bea curing, drying and/or crosslinking step. A curing or crosslinking stepmay, in some cases, allow for curing of only a desired polymer pattern.The curing or crosslinking step may include photo-initiated techniques,such as ultraviolet (UV) curing/crosslinking, plasma treatment, and/orelectron beam curing/crosslinking. In some embodiments, the polymermasking and/or curing/crosslinking/drying steps may be conducted undervacuum. Crosslinking steps may involve the use of photoinitiators.

In some embodiments, the bulk, shear, and/or Young's modulus of acomposite structure comprising material-filled cavities in a matrix(e.g., inorganic material-filled cavities in a polymer matrix, or viceversa) may be less than an analogous modulus of a comparative compositestructure comprising a first layer of the inorganic material and asecond layer of the polymer. For example, a first composite comprisinginorganic material-filled cavities in a polymer matrix may have anoverall thickness, a total amount of inorganic material, and a totalamount of polymer. A second, comparative composite comprising a firstlayer of the inorganic material and a second layer of the polymer mayhave the same overall thickness, the same total amount of inorganicmaterial, and the same total amount of polymer. The first composite mayhave a bulk, shear, and/or Young's modulus that is less (e.g., by atleast a factor of about 2, at least a factor of about 10, at least afactor of about 20, at least a factor of about 50, or at least a factorof about 100, in some embodiments up to a factor of 1000, or up to afactor of 500) than the analogous modulus for the second, comparativecomposite. A bulk, shear, and/or Young's modulus for the first compositethat is lower than the analogous modulus for the second composite mayindicate that the first composite is more flexible and/or deformablethan the second composite. The bulk, shear, and/or Young's modulus maybe determined for each composite according to any method known in theart. For example, the international standard ISO 14577-4:2007 (E) testmethod (test method for metallic and non-metallic coatings) may be usedto determine the Young's modulus of each of the first and secondcomposites.

In some embodiments, the bulk, shear, and/or Young's modulus of at leastone polymer in the polymer matrix of a composite layer may be less thanthe analogous modulus of at least one inorganic material (e.g., ceramicmaterial) in the layer (e.g., filling at least one cavity in the polymermatrix) by at least a factor of about 2, at least a factor of about 10,at least a factor of about 20, at least a factor of about 50, or atleast a factor of about 100, in some embodiments up to a factor of 1000,or up to a factor of 500. A lower polymer modulus compared to theinorganic material (e.g., ceramic) modulus may result in a compositelayer that is more robust and/or more flexible than the inorganicmaterial (e.g., ceramic) alone. The international standard ISO14577-4:2007 (E) test method (test method for metallic and non-metalliccoatings) may be used.

In some embodiments, the fracture strain of a composite structurecomprising material-filled cavities in a matrix (e.g., inorganicmaterial-filled cavities in a polymer matrix, or vice versa) may belarger than the fracture strain of a composite structure comprising afirst layer of the inorganic material and a second layer of the polymer.For example, a first composite comprising inorganic material-filledcavities in a polymer matrix may have an overall thickness, a totalamount of inorganic material, and a total amount of polymer. A secondcomposite comprising a first layer of the inorganic material and asecond layer of the polymer may have the same overall thickness, thesame total amount of inorganic material, and the same total amount ofpolymer. The first composite may have a fracture strain larger than thefracture strain of the second composite, e.g., by at least a factor ofabout 2, at least a factor of about 10, at least a factor of about 20,at least a factor of about 50, or at least a factor of about 100, insome embodiments up to a factor of 1000, or up to a factor of 500. Afracture strain for the first composite that is larger than the fracturestrain for the second composite may indicate that the first composite isable to withstand more strain prior to fracture than the secondcomposite. The fracture strain may be determined for each compositeaccording to any method known in the art. For example, the standard ASTME2546-07 may be used.

In some embodiments, the fracture strain of at least one polymer in thepolymer matrix may be larger than the fracture strain of at least oneinorganic material (e.g., ceramic material) in the layer (e.g., fillingat least one cavity in the polymer matrix) by at least a factor of about2, at least a factor of about 10, at least a factor of about 20, atleast a factor of about 50, or at least a factor of about 100, in someembodiments up to a factor of 1000, or up to a factor of 500. A higherpolymer fracture strain compared to the inorganic material (e.g.,ceramic) fracture strain may result in a composite layer that is able towithstand more strain prior to fracture than the inorganic material(e.g., ceramic) alone. In some embodiments, the standard ASTM E2546-07may be used.

In some embodiments, the critical radius of curvature of a compositestructure comprising material-filled cavities in a matrix (e.g.,inorganic material-filled cavities in a polymer matrix, or vice versa)may be larger than the critical radius of curvature of a compositestructure comprising a first layer of the inorganic material and asecond layer of the polymer. For example, a first composite structurecomprising material-filled cavities in a matrix (e.g., inorganicmaterial-filled cavities in a polymer matrix, or vice versa) may have anoverall thickness, a total amount of inorganic material, and a totalamount of polymer. A second, comparative composite comprising a firstlayer of the inorganic material and a second layer of the polymer mayhave the same overall thickness, the same total amount of inorganicmaterial, and the same total amount of polymer. The first composite mayhave a critical radius of curvature larger than the critical radius ofcurvature of the second composite, e.g., by at least a factor of about2, at least a factor of about 10, at least a factor of about 20, atleast a factor of about 50, or at least a factor of about 100, in someembodiments up to a factor of 1000, or up to a factor of 500. A criticalradius of curvature for the first composite that is larger than thecritical radius of curvature for the second composite may indicate thatthe first composite is more flexible than the second composite. Thecritical radius of curvature may be determined for each compositeaccording to any method known in the art. For example, the criticalradius of curvature may be determined using a bending test. Such a testmay involve obtaining a sample (e.g. a sample having dimensions of 5cm×2.5 cm). The geometric center of the sample is determined by opticalprofilometry. The edges of the sample are moved together, causing thesample to be bent into the shape of an arc. For example, for a samplehaving a length of 5 cm, the edges of the sample may be moved todistances ranging from about 4.5 cm (e.g., a slight change, orrelatively small radius of curvature) to about 2.5 cm (e.g., a severechange, or relatively large radius of curvature). At differentdistances, the radius of curvature of the sample may be measured, andthe presence or absence of fractures may be determined by opticalprofilometry at the geometric center. The critical radius of curvatureis the minimum radius of curvature at which fracture begins to takeplace at the geometric center of the sample.

In certain embodiments, the critical radius of curvature of at least onepolymer in the polymer matrix is less than the critical radius ofcurvature of at least one inorganic material (e.g., ceramic material)filling at least one cavity in the polymer matrix by a factor of about2, about 10, about 20, about 50, or about 100. The critical radius ofcurvature may be determined using a bending test, e.g., as describedabove.

The polymer layer or polymeric portions within a composite layer can beconfigured to be substantially electronically non-conductive, in certainembodiments, which can inhibit the degree to which the polymer layercauses short circuiting of the electrochemical cell. In certainembodiments, all or part of the polymer portions can be formed of amaterial with a bulk electronic resistivity of at least about 10⁴, atleast about 10⁵, at least about 10¹⁰, at least about 10¹⁵, or at leastabout 10²⁰ Ohm-meters. The bulk resistivity may be, for example, lessthan about 10⁵⁰ Ohm-meters, less than about 10⁴⁰ Ohm-meters, or lessthan about 10²⁰ Ohm-meters. In other embodiments, electronicallyconductive polymers can be used. Combinations of the above-referencedranges are also possible. In some embodiments, the polymer may consistessentially of one or more polymers. The polymer may, in someembodiments, be a monomer, a mixture of copolymers, block copolymers, ora combination of two or more polymers that are in an interpenetratingnetwork or semi-interpenetrating network. In alternative embodiments,the polymer may comprise a filler and/or solid additive. The fillerand/or solid additive may add strength, flexibility, and/or improvedadhesion properties to the polymer. In some embodiments, the polymer maycomprise a plasticizer or other additives, including solid phase changematerials. Addition of plasticizers may increase flexibility of thepolymer and improve thixotropic properties. Addition of solid phasechange materials may result in addition of materials that melt atelevated temperatures and thereby act as a heat sink and prevent thermalrunaway.

In some embodiments, the polymer may be selected to be flexible.Nano-hardness studies may be conducted to measure creep and/or hardnessand thereby assess the flexibility and/or brittleness of a polymer. Incertain cases, the polymer may be selected to be thermally stable above200° C., 250° C., 300° C., 350° C., or 400° C. Thermal stability may beassessed by differential scanning calorimetry (DSC). Non-limitingexamples of polymers that may exhibit thermal stability at elevatedtemperatures include polysiloxanes, polycyanurates, andpolyisocyanurates.

In some embodiments, the polymer may be selected to exhibit goodadhesion to the inorganic material (e.g., ceramic, glass, orglassy-ceramic material). Adhesion may be assessed by a peel force test.In certain embodiments, to determine relative adhesion strength betweentwo materials (e.g., two layers of materials), a tape test can beperformed. Briefly, the tape test utilizes pressure-sensitive tape toqualitatively asses the adhesion between a first layer (e.g., a polymerlayer) and a second layer (e.g., an inorganic material layer). In such atest, an X-cut can be made through the first layer (e.g., polymer layer)to the second layer (e.g., an inorganic material layer).Pressure-sensitive tape can be applied over the cut area and removed. Ifthe polymer layer stays on the inorganic material layer, adhesion isgood. If the polymer layer comes off with the strip of tape, adhesion ispoor. The tape test may be performed according to the standard ASTMD3359-02. In some embodiments, a strength of adhesion between thepolymeric material and the inorganic material passes the tape testaccording to the standard ASTM D3359-02, meaning the inorganic materialdoes not delaminate from the polymer material (or vice versa) during thetest.

Examples of polymers that may offer good adhesion to inorganicmaterials/ceramics include, but are not limited to, polysiloxanes, whichmay provide flexibility and strength. The polymer may, in certain cases,be selected to be inert to the electrolyte solution and/or Lipolysulfide attack. A means of determining the stability of a polymer inan electrolyte solution includes exposing a small sample of the polymerto vapors of an electrolyte solvent. Examples of polymers that may bestable in an electrolyte solution include, but are not limited to,polyurethanes and polysiloxanes. Additional tests that may be conductedon polymers to examine various characteristics include Fourier transforminfrared spectroscopy (FTIR) to confirm that a polymer is cured orcrosslinked, scanning electron microscopy with energy dispersive x-rayspectroscopy (SEM-EDS) to determine whether a polymer has cracks. Suchtest and other tests can also be used to determine whether a compositelayer comprises discrete layers, interpenetrating networks, orsemi-interpenetrating networks. Profilometry can be used to assess howrough the surface of a polymer is, and whether cracks are formed fromdeposition of the inorganic material (e.g., ceramic material).

Other classes polymers that may be suitable for use in a polymer layeror as polymeric portions include, but are not limited to, polyamines(e.g., poly(ethylene imine) and polypropylene imine (PPI)); polyamides(e.g., polyamide (Nylon), poly(ϵ-caprolactam) (Nylon 6),poly(hexamethylene adipamide) (Nylon 66)), polyimides (e.g., polyimide,polynitrile, and poly(pyromellitimide-1,4-diphenyl ether) (Kapton));vinyl polymers (e.g., polyacrylamide, poly(2-vinyl pyridine),poly(N-vinylpyrrolidone), poly(methylcyanoacrylate),poly(ethylcyanoacrylate), poly(butylcyanoacrylate),poly(isobutylcyanoacrylate), poly(vinyl acetate), poly (vinyl alcohol),poly(vinyl chloride), poly(vinyl fluoride), poly(2-vinyl pyridine),vinyl polymer, polychlorotrifluoro ethylene, andpoly(isohexylcynaoacrylate)); polyacetals; polyolefins (e.g.,poly(butene-1), poly(n-pentene-2), polypropylene,polytetrafluoroethylene); polyesters (e.g., polycarbonate, polybutyleneterephthalate, polyhydroxybutyrate); polyethers (poly(ethylene oxide)(PEO), poly(propylene oxide) (PPO), poly(tetramethylene oxide) (PTMO));vinylidene polymers (e.g., polyisobutylene, poly(methyl styrene),poly(methylmethacrylate) (PMMA), poly(vinylidene chloride), andpoly(vinylidene fluoride)); polyaramides (e.g., poly(imino-1,3-phenyleneiminoisophthaloyl) and poly(imino-1,4-phenylene iminoterephthaloyl));polyheteroaromatic compounds (e.g., polybenzimidazole (PBI),polybenzobisoxazole (PBO) and polybenzobisthiazole (PBT));polyheterocyclic compounds (e.g., polypyrrole); polyurethanes; phenolicpolymers (e.g., phenol-formaldehyde); polyalkynes (e.g., polyacetylene);polydienes (e.g., 1,2-polybutadiene, cis or trans-1,4-polybutadiene);polysiloxanes (e.g., poly(dimethylsiloxane) (PDMS),poly(diethylsiloxane) (PDES), polydiphenylsiloxane (PDPS), andpolymethylphenylsiloxane (PMPS)); and inorganic polymers (e.g.,polyphosphazene, polyphosphonate, polysilanes, polysilazanes). In someembodiments, the polymer may be selected from the group consisting ofpolyvinyl alcohol, polyisobutylene, epoxy, polyethylene, polypropylene,polytetrafluoroethylene, and combinations thereof. The mechanical andelectronic properties (e.g., conductivity, resistivity) of thesepolymers are known.

Accordingly, those of ordinary skill in the art can choose suitablepolymers based on their mechanical and/or electronic properties (e.g.,ionic and/or electronic conductivity), and/or can modify such polymersto be ionically conducting (e.g., conductive towards single ions) and/orelectronically conducting based on knowledge in the art, in combinationwith the description herein. For example, the polymer materials listedabove may further comprise salts, for example, lithium salts (e.g.,LiSCN, LiBr, LiI, LiClO₄, LiAsF₆, LiSO₃CF₃, LiSO₃CH₃, LiBF₄, LiB(Ph)₄,LiPF₆, LiC(SO₂CF₃)₃, and LiN(SO₂CF₃)₂), to enhance ionic conductivity.Salts may be added to the a material at a range of, e.g., 0 to 50 mol %.In certain embodiments, salts are included in at least 5 mol %, at least10 mol %, at least 20 mol %, at least 30 mol %, at least 40 mol %, or atleast 50 mol % of the material. In certain embodiments, additional saltsare less than or equal to 50 mol %, less than or equal to 40 mol %, lessthan or equal to 30 mol %, less than or equal to 20 mol %, or less thanor equal to 10 mol % of the material. Combinations of the above-notedranges are also possible. Other values of mol % are also possible.

In some embodiments, the polymer can be ionically conductive, while inother embodiments, the polymer is substantially ionicallynon-conductive. In some embodiments, the average ionic conductivity ofthe polymer is at least about 10⁻⁷ S/cm, at least about 10⁻⁶ S/cm, atleast about 10⁻⁵ S/cm, at least about 10⁻⁴ S/cm, at least about 10⁻²S/cm, at least about 10⁻¹ S/cm. In certain embodiments, the averageionic conductivity of the polymer may be less than or equal to about 1S/cm, less than or equal to about 10⁻¹ S/cm, less than or equal to about10⁻² S/cm, less than or equal to about 10⁻³ S/cm, less than or equal toabout 10⁻⁴ S/cm, less than or equal to about 10⁻⁵ S/cm, less than orequal to about 10⁻⁶ S/cm, less than or equal to about 10⁻⁷ S/cm, or lessthan or equal to about 10⁻⁸ S/cm. Combinations of the above-referencedranges are also possible (e.g., an average ionic conductivity of atleast about 10⁻⁸ S/cm and less than or equal to about 10⁻¹ S/cm).Conductivity may be measured at room temperature (e.g., 25 degreesCelsius).

The selection of an appropriate polymer may depend on a number offactors, including the properties of the electrolyte and the anode andcathode used in the electrochemical cell.

In some embodiments, the polymer may be ionically and electronicallyconductive. Examples of such polymers include, but are not limited to,electrically conductive polymers (also known as electronic polymers orconductive polymers) that are doped with lithium salts (e.g., LiSCN,LiBr, LiI, LiClO₄, LiAsF₆, LiSO₃CF₃, LiSO₃CH₃, LiBF₄, LiB(Ph)₄, LiPF₆,LiC(SO₂CF₃)₃, and LiN(SO₂CF₃)₂). Conductive polymers are known in theart; examples of such polymers include, but are not limited to,poly(acetylene)s, poly(pyrrole)s, poly(thiophene)s, poly(aniline)s,poly(fluorene)s, polynaphthalenes, poly(p-phenylene sulfide), andpoly(para-phenylene vinylene)s. Electrically-conductive additives mayalso be added to polymers to form electrically-conductive polymers.Certain electrically conductive materials may have a conductivity of,e.g., greater than 10⁻² S/cm, greater than 10⁻¹ S/cm, greater than 1S/cm, greater than 10¹ S/cm, greater than 10² S/cm, greater than 10³S/cm, greater than 10⁴ S/cm, or greater than 10⁵ S/cm.

In some embodiments, the polymer may be ionically conductive butsubstantially non-electrically conductive. Examples of such polymersinclude non-electrically conductive materials (e.g., electricallyinsulating materials) that are doped with lithium salts, such asacrylate, polyethylene oxide, silicones, and polyvinyl chlorides.

In some embodiments, the polymeric material included in a compositelayer or protective structure is substantially non-swellable in anelectrolyte solvent to be used in an electrochemical cell including sucha composite layer or protective structure. For instance, the polymericmaterial may experience a volume change of less than 10%, less than 8%,less than 6%, less than 4%, less than 2%, or less than 1% when incontact with an electrolyte solvent (including any salts or additivespresent) to be used in an electrochemical cell including such acomposite layer or protective structure for at least 24 hours. Simplescreening tests of such polymers can be conducted by placing pieces ofpolymer in the electrolyte solvent (including any salts or additivespresent) and measuring the volume change of the polymer pieces beforeand after a 24 hour period, and determining the percentage change involume relative to the volume before placement in the solvent.

Inorganic material portions or an inorganic material layer describedherein (which may be continuous or discontinuous) can be formed of avariety of types of materials. In certain embodiments, the material fromwhich the inorganic material portions/layers is formed may be selectedto allow ions (e.g., electrochemically active ions, such as lithiumions) to pass through the material but to substantially impede electronsfrom passing across the material. By “substantially impedes”, in thiscontext, it is meant that in this embodiment the material allows lithiumion flux at least ten times greater than electron passage.

In some embodiments, the material used for an inorganic material portionor layer has a high enough conductivity (e.g., at least 10⁻⁶ S/cm, oranother conductivity value described herein) in its first amorphousstate. The material may also be chosen for its ability to form smooth,dense and homogenous thin portions or films, especially on a polymerportion or layer.

The inorganic material (e.g., ceramic) can be configured to besubstantially electronically non-conductive, in certain embodiments,which can inhibit the degree to which the material causes shortcircuiting of the electrochemical cell. In certain embodiments, all orpart of the inorganic material portions or layer can be formed of amaterial with a bulk electronic resistivity of at least about 10⁴Ohm-meters, at least about 10⁵ Ohm-meters, at least about 10¹⁰Ohm-meters, at least about 10¹⁵ Ohm-meters, or at least about 10²⁰Ohm-meters. The bulk electronic resistivity may be, in some embodiments,less than or equal to about 10²⁰ Ohm-meters, or less than or equal toabout 10¹⁵ Ohm-meters. Combinations of the above-referenced ranges arealso possible. Other values of bulk electronic resistivity are alsopossible.

In some embodiments, the average ionic conductivity (e.g., metal ion,such as lithium ion, conductivity) of the inorganic material portion orlayer (e.g., ceramic) is at least about 10⁻⁷ S/cm, at least about 10⁻⁶S/cm, at least about 10⁻⁵ S/cm, at least about 10⁻⁴ S/cm, at least about10⁻³ S/cm, at least about 10⁻² S/cm, at least about 10 S/cm, at leastabout 1 S/cm, or at least about 10 S/cm. The average ionic conductivitymay less than or equal to about 20 S/cm, less than or equal to about 10S/cm, or less than or equal to 1 S/cm. Conductivity may be measured atroom temperature (e.g., 25 degrees Celsius).

Inorganic materials described herein (e.g., ceramics, glasses, orglassy-ceramic materials) may be deposited within a polymer matrix byany suitable method such as sputtering (including, but not limited to,diode, DC magnetron, RF, RF magnetron, pulsed, dual magnetron, AC, MF,and reactive), electron beam evaporation, vacuum thermal evaporation(including, but not limited to, resistive, inductive, radiation, andelectron beam heating), laser ablation, chemical vapor deposition (CVD),thermal evaporation, plasma enhanced chemical vacuum deposition (PECVD),laser enhanced chemical vapor deposition, and jet vapor deposition.

Deposition of the polymer and/or inorganic material may be carried outin a vacuum or inert atmosphere to minimize side reactions in thedeposited layers that could introduce impurities into the layers orwhich may affect the desired morphology of the layers. In someembodiments, the deposition of the polymer and/or inorganic material iscarried out under atmospheric conditions.

In some embodiments, the inorganic material (e.g., ceramic) may includea glass conductive to metal ions. Suitable glasses include, but are notlimited to, those that may be characterized as containing a “modifier”portion and a “network” portion, as known in the art. The modifier mayinclude a metal oxide of the metal ion conductive in the glass. Thenetwork portion may include a metal chalcogenide such as, for example, ametal oxide or sulfide.

In some embodiments, the inorganic material (e.g., ceramic) may comprisea material including one or more of lithium nitrides, lithium silicates,lithium borates, lithium aluminates, lithium phosphates, lithiumphosphorus oxynitrides, lithium silicosulfides, lithium germanosulfides,lithium oxides (e.g., Li₂O, LiO, LiO₂, LiRO₂, where R is a rare earthmetal), lithium lanthanum oxides, lithium titanium oxides, lithiumborosulfides, lithium aluminosulfides, and lithium phosphosulfides,oxy-sulfides (e.g., lithium oxy-sulfides) and combinations thereof. Insome embodiments, the inorganic material (e.g., ceramic) may compriseAl₂O₃, ZrO₂, SiO₂, CeO₂, and/or Al₂TiO₅. The selection of the inorganicmaterial (e.g., ceramic) will be dependent on a number of factorsincluding, but not limited to, the properties of electrolyte and theanode and cathode used in the cell.

Those of ordinary skill in the art, given the present disclosure, wouldbe capable of selecting appropriate materials for use as polymericportions or inorganic material portions or layers. Relevant factors thatmight be considered when making such selections include the ionicconductivity of the materials; the ability to deposit or otherwise formthe material on or with other materials in the electrochemical cell; theflexibility of the material; the porosity or non-porosity of thematerial (e.g., overall porosity, pore size distribution, and/ortortuosity); the compatibility of the material with the fabricationprocess used to form the electrochemical cell; the compatibility of thematerial with the electrolyte of the electrochemical cell; and/or theability to adhere the material to another material or layer. In certainembodiments, the material can be selected based on its ability tosurvive deposition processes without mechanically failing. For example,in embodiments in which relatively high temperatures or high pressuresare used to form the ion conductor material (e.g., a ceramic ionconductor material), a polymer material can be selected or configured towithstand such high temperatures and pressures.

Those of ordinary skill in the art can employ a simple screening test toselect an appropriate material from candidate materials. One simplescreening test involves positioning a material in an electrochemicalcell which, to function, requires passage of an ionic species across thematerial while maintaining electronic separation. This is a simple testto employ. If the material is substantially ionically conductive in thistest, then electrical current will be generated upon discharging theelectrochemical cell. A screening test may also involve testing theadhesion between polymeric and inorganic material portions as describedherein. Another screening test may involve testing the ability of thepolymer to not swell in the presence of an electrolyte to be used in anelectrochemical cell. Other simple tests can be conducted by those ofordinary skill in the art.

The inorganic material portions of a composite layer described hereinmay, in some embodiments, be isolated regions within the layer (i.e.,they may be discontinuous regions within the layer). In otherembodiments, the inorganic material portions form a continuous layer.

As noted above, the electrode and/or protective structures describedherein may be arranged in an electrochemical cell comprising anelectrolyte. The electrolytes used in electrochemical or battery cellscan function as a medium for the storage and transport of ions, and inthe special case of solid electrolytes and gel electrolytes, thesematerials may additionally function as a separator between the anode andthe cathode. Any liquid, solid, or gel material capable of storing andtransporting ions may be used, so long as the material facilitates thetransport of ions (e.g., lithium ions) between the anode and thecathode. The electrolyte is electronically non-conductive to preventshort circuiting between the anode and the cathode. In some embodiments,the electrolyte may comprise a non-solid electrolyte. Suitablenon-aqueous electrolytes may include organic electrolytes comprising oneor more materials selected from the group consisting of liquidelectrolytes, gel polymer electrolytes, and solid polymer electrolytes.

Examples of useful non-aqueous liquid electrolyte solvents include, butare not limited to, non-aqueous organic solvents, such as, for example,N-methyl acetamide, acetonitrile, acetals, ketals, esters, carbonates,sulfones, sulfites, sulfolanes, aliphatic ethers, acyclic ethers, cyclicethers, glymes, polyethers, phosphate esters, siloxanes, dioxolanes,N-alkylpyrrolidones, substituted forms of the foregoing, and blendsthereof. Examples of acyclic ethers that may be used include, but arenot limited to, diethyl ether, dipropyl ether, dibutyl ether,dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane,1,2-dimethoxypropane, and 1,3-dimethoxypropane. Examples of cyclicethers that may be used include, but are not limited to,tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran, 1,4-dioxane,1,3-dioxolane, and trioxane. Examples of polyethers that may be usedinclude, but are not limited to, diethylene glycol dimethyl ether(diglyme), triethylene glycol dimethyl ether (triglyme), tetraethyleneglycol dimethyl ether (tetraglyme), higher glymes, ethylene glycoldivinylether, diethylene glycol divinylether, triethylene glycoldivinylether, dipropylene glycol dimethyl ether, and butylene glycolethers. Examples of sulfones that may be used include, but are notlimited to, sulfolane, 3-methyl sulfolane, and 3-sulfolene. Fluorinatedderivatives of the foregoing are also useful as liquid electrolytesolvents. Mixtures of the solvents described herein can also be used. Insome cases, aqueous solvents can be used as electrolytes for lithiumcells. Aqueous solvents can include water, which can contain othercomponents such as ionic salts. In some embodiments, the electrolyte caninclude species such as lithium hydroxide, or other species renderingthe electrolyte basic, so as to reduce the concentration of hydrogenions in the electrolyte.

Liquid electrolyte solvents can also be useful as plasticizers for gelpolymer electrolytes, i.e., electrolytes comprising one or more polymersforming a semi-solid network. Examples of useful gel polymerelectrolytes include, but are not limited to, those comprising one ormore polymers selected from the group consisting of polyethylene oxides,polypropylene oxides, polyacrylonitriles, polysiloxanes, polyimides,polyphosphazenes, polyethers, sulfonated polyimides, perfluorinatedmembranes (NAFION resins), polydivinyl polyethylene glycols,polyethylene glycol diacrylates, polyethylene glycol dimethacrylates,derivatives of the foregoing, copolymers of the foregoing, crosslinkedand network structures of the foregoing, and blends of the foregoing,and optionally, one or more plasticizers. In some embodiments, a gelpolymer electrolyte comprises between 10-20%, 20-40%, between 60-70%,between 70-80%, between 80-90%, or between 90-95% of a heterogeneouselectrolyte by volume.

In some embodiments, one or more solid polymers can be used to form anelectrolyte. Examples of useful solid polymer electrolytes include, butare not limited to, those comprising one or more polymers selected fromthe group consisting of polyethers, polyethylene oxides, polypropyleneoxides, polyimides, polyphosphazenes, polyacrylonitriles, polysiloxanes,derivatives of the foregoing, copolymers of the foregoing, crosslinkedand network structures of the foregoing, and blends of the foregoing.

In addition to electrolyte solvents, gelling agents, and polymers asknown in the art for forming electrolytes, the electrolyte may furthercomprise one or more ionic electrolyte salts, also as known in the art,to increase the ionic conductivity.

Examples of ionic electrolyte salts for use in the electrolytes of thepresent invention include, but are not limited to, LiSCN, LiBr, LiI,LiClO₄, LiAsF₆, LiSO₃CF₃, LiSO₃CH₃, LiBF₄, LiB(Ph)₄, LiPF₆,LiC(SO₂CF₃)₃, and LiN(SO₂CF₃)₂. Other electrolyte salts that may beuseful include lithium polysulfides (Li₂Sx), and lithium salts oforganic ionic polysulfides (LiSxR)_(n), where x is an integer from 1 to20, n is an integer from 1 to 3, and R is an organic group.

As described herein, in some embodiments, an electrolyte may be presentas a polymer layer adjacent a protective structure (e.g., on a sideopposite the electroactive layer). The polymer layer may be, in someembodiments, a gel polymer layer. In some cases, in addition to beingable to function as a medium for the storage and transport of ions, apolymer layer positioned between an anode and cathode can function toscreen the anode (e.g., a base electrode layer of the anode) from anycathode roughness under an applied force or pressure, keeping the anodesurface smooth under force or pressure, and/or stabilizing anyprotective structures of the anode by keeping the protective structurepressed between the base electrode layer and the electrolyte layer. Insome such embodiments, the polymer layer may be chosen to be compliantand have a smooth surface.

An electrolyte layer including a gel may have a three-dimensionalnetwork comprising a liquid and a binder component, in which the liquidis entrained by and not allowed to flow through the binder. Gels can beformed when liquids are entrained within a three-dimensional network ofsolids upon applying the liquid to the solid network. In some cases, thethree-dimensional network within a gel can comprise a liquid entrainedwithin a polymer (e.g., a cross-linked polymer). One of ordinary skillin the art would be capable of determining the difference between a geland other combinations of a solid and a fluid (e.g., a porous separatorand a liquid solvent) by measuring, for example, the absorptionstiffness of the gel via a dibutyl phthalate (DBP) uptake test. For thistest, a dry sample of the binder material is weighed. The weighed sampleis immersed in DBP for 30 min. The excess DBP is removed by absorbentpaper and the sample is weighed again. Generally, upon exposure of thebinder component of a gel to a liquid, the weight of the gel willincrease, while the weight of a porous separator will not substantiallyincrease. In some embodiments, the binder component of the gel is ableto take up liquid in the substantial absence of pores greater than about10 microns or greater than about 1 micron. The binder component of a gelcan be substantially free of pores in some cases.

In some embodiments, an electrolyte comprising a polymer gel is formedby using a hard ionically conductive polymer and optionally swelling atleast a portion of the polymer in a solvent to form a gel. In anotherembodiment, a mixture of hard and softer polymers can be used, in whichat least one, or both, of such polymers is ionically conductive. Inanother embodiment, an electrolyte includes a rigid, non-swellingscaffold (e.g., like a standard separator as described herein), which isfilled with a polymer, such as a conductive polymer. The above-notedembodiments may optionally include particles (e.g., silica particlesadded to the polymers). In some embodiments, the above-noted embodimentsmay optionally include some degree of crosslinking. The polymers may beswollen in a solvent as described herein.

In some embodiments, a polymer gel may include a polyethersulfone.Polyethersulfones are polymeric materials that exhibit SO₂ groups(sulfonyl groups) and oxygen atoms that form part of ether groups intheir constitutional repeating units. Polyethersulfones can bealiphatic, cycloaliphatic or aromatic polyethersulfones. In certainembodiments, one or more branched polyimide, polyvinylalcohol or a blendof polyvinylalcohol (PVOH) and additional (co)polymer(s) can be used.

A polymer electrolyte gel may include, in some embodiments, materialsbased on a polymer (e.g., non-porous polyvinylalcohol) as a non-fluidmaterial swollen with a solvent having affinity to the polymer. E.g.,for PVOH, the solvent may include dimethylacetamide (DMAc),N-methylpyrolidone (NMP), dimethylsulfoxide (DMSO), dimethylformamide(DMF), sulfolanes and/or sulfones. In certain embodiments, the polymermay be swollen in a solvent mixture comprising a solvent having affinityto polymer and also solvents having no affinity to the polymer(so-called non-solvents) such as, for PVOH, 1,2.dimethoxyethane (DME),diglyme, triglyme, 1,3-dioxolane (DOL), THF, 1,4-dioxane, cyclic andlinear ethers, esters (carbonates as dimethylcarbonate and ethylenecarbonate), acetals and ketals. The solvents for preparing the polymergel may be selected from the solvents described herein and may compriseelectrolyte salts, including lithium salts selected from the lithiumsalts described herein.

In certain embodiments, polymer electrolyte gels may be prepared frombranched and hyperbranched polyimides. Hyperbranched polyimides are asubclass of branched polyimides. They are composed of highly branchedmacromolecules in which any linear subchain may lead in either directionto at least two other subchains.

In other embodiments, polymer electrolyte gels may be prepared materialssuch as cyanoethylated cellulose, polyether ether ketones and sulfonatedpolyether ether ketones.

In some embodiments a polymer gel is crosslinked with a suitablecross-linker. Examples of cross-linkers may include ones selected frommolecules with two or more carbon-carbon double bonds, e.g., ones withtwo or more vinyl groups. Particularly useful cross-linkers are selectedfrom di(meth)acrylates of diols such as glycol, propylene glycol,diethylene glycol, dipropylene glycol, 1,3-propanediol, 1,4-butanediol,triethylene glycol, tetrapropylene glycol, cyclopentadiene dimer,1,3-divinyl benzene, and 1,4-divinyl benzene. Some suitablecross-linkers may comprise two or more epoxy groups in the molecule,such as, for example, bis-phenol F, bis-phenol A, 1,4-butanedioldiglycidyl ether, glycerol propoxylate triglycidyl ether, and the like.Cross-linking can be achieved by, for example, adding cross-linker to apolymer and performing a cross-linking reaction, e.g., by thermal orphotochemical curing, e.g. by irradiation with such as UV/visirradiation, by γ-irradiation, electron beams (e-beams) or by heating(thermal cross-linking).

In some embodiments, one or more solid polymers can be used to form anelectrolyte. Examples of useful solid polymer electrolytes include, butare not limited to, those comprising one or more polymers selected fromthe group consisting of polyethers, polyethylene oxides, polypropyleneoxides, polyimides, polyphosphazenes, polyacrylonitriles, polysiloxanes,derivatives of the foregoing, copolymers of the foregoing, crosslinkedand network structures of the foregoing, and blends of the foregoing.

In some embodiments, an electrolyte layer described herein may have athickness of at least 1 micron, at least 5 microns, at least 10 microns,at least 15 microns, at least 20 microns, at least 25 microns, at least30 microns, at least 40 microns, at least 50 microns, at least 70microns, at least 100 microns, at least 200 microns, at least 500microns, or at least 1 mm. In some embodiments, the thickness of theelectrolyte layer is less than or equal to 1 mm, less than or equal to500 microns, less than or equal to 200 microns, less than or equal to100 microns, less than or equal to 70 microns, less than or equal to 50microns, less than or equal to 40 microns, less than or equal to 30microns, less than or equal to 20 microns, less than or equal to 10microns, or less than or equal to 50 microns. Other values are alsopossible. Combinations of the above-noted ranges are also possible.

The protected electrode structures described herein may apply to ananode or cathode.

In some embodiments, the electrode may be arranged in an electrochemicalcell. That cell, in certain cases, may be a primary (non-rechargeable)battery. In other cases, the electrochemical cell may be a secondary(rechargeable) battery. Many embodiments described herein involvelithium rechargeable batteries. However, wherever lithium batteries aredescribed herein, it is to be understood that any analogous alkali metalbattery can be used. Additionally, although embodiments of the inventionare particularly useful for protection of a lithium anode, the presentinvention may be applicable to other applications in which electrodeprotection is desired.

The electrode described herein may comprise a base layer comprising anactive electrode species. In certain cases, the electrode is an anode.The anode, in some embodiments, comprises lithium. The anode maycomprise or be formed of lithium metal. The lithium metal may be in theform of, e.g., a lithium metal foil or a thin lithium film that has beendeposited on a substrate. The lithium metal may also be in the form of alithium alloy, such as, for example, a lithium-tin alloy or alithium-aluminum alloy. In some embodiments, lithium metal may bedeposited (e.g., vacuum deposited) directly onto a protective structuredescribed herein.

In some embodiments, the electrode is a cathode. Suitable cathode activematerials for use in the cathode of the electrochemical cells of theinvention include, but are not limited to, electroactive transitionmetal chalcogenides, electroactive conductive polymers, andelectroactive sulfur-containing materials, and combinations thereof. Asused herein, the term “chalcogenides” pertains to compounds that containone or more of the elements of oxygen, sulfur, and selenium. Examples ofsuitable transition metal chalcogenides include, but are not limited to,the electroactive oxides, sulfides, and selenides of transition metalsselected from the group consisting of Mn, V, Cr, Ti, Fe, Co, Ni, Cu, Y,Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, and Ir. In oneembodiment, the transition metal chalcogenide is selected from the groupconsisting of the electroactive oxides of nickel, manganese, cobalt, andvanadium, and the electroactive sulfides of iron. In certainembodiments, the cathode may include as an electroactive specieselemental sulfur, sulfides, and/or polysulfides. In other embodiments,an intercalation electrode (e.g., a lithium-intercalation cathode) maybe used. Non-limiting examples of suitable materials that mayintercalate ions of an electroactive material (e.g., alkaline metalions) include oxides, titanium sulfide, and iron sulfide. Additionalexamples include LixCoO₂, Li_(x)NiO₂, LixMnO₂, LixMn₂O₄, Li_(x)FePO₄,Li_(x)CoPO₄, Li_(x)MnPO₄, and Li_(x)NiPO₄, where (0<x≤1), andLiNi_(x)Mn_(y)Co_(z)O₂ where (x+y+z=1).

In one embodiment, the cathode active layer comprises an electroactiveconductive polymer. Examples of suitable electroactive conductivepolymers include, but are not limited to, electroactive andelectronically conductive polymers selected from the group consisting ofpolypyrroles, polyanilines, polyphenylenes, polythiophenes, andpolyacetylenes. In some embodiments, the conductive polymer may be oneor more of polypyrroles, polyanilines, and polyacetylenes.

In some embodiments, the electrode is arranged in an electrochemicalcell that comprises an electrolyte. The electrolyte can comprise one ormore ionic electrolyte salts to provide ionic conductivity and one ormore liquid electrolyte solvents, gel polymer materials, or polymermaterials. Examples of suitable electrolytes are provided in furtherdetail below.

In some embodiments, the electrode may comprise a gel layer (e.g., a gelelectrolyte) between the base layer comprising an active species and theprotective structure comprising a polymer and an inorganic material. Theprotective structure may, in some cases, be in direct contact with agel, an electrolyte, a separator positioned between the anode and thecathode, and/or a temporary carrier substrate in an electrochemicalcell.

In some embodiments, there may be a substrate on one side of theelectrode. Substrates may be useful as a support on which to deposit theelectrode active material, and they may provide additional stability forhandling during cell fabrication. Further, in the case of conductivesubstrates, a substrate may also function as a current collector usefulin efficiently collecting the electrical current generated throughoutthe electrode and in providing an efficient surface for attachment ofelectrical contacts leading to an external circuit. Suitable substratesinclude, but are not limited to, those selected from the groupconsisting of metal foils, polymer films, metallized polymer films,electrically conductive polymer films, polymer films having anelectrically conductive coating, electrically conductive polymer filmshaving an electrically conductive metal coating, and polymer filmshaving conductive particles dispersed therein. In one embodiment, thesubstrate is a metallized polymer film. In other embodiments, describedmore fully below, the substrate may be selected fromnon-electrically-conductive materials. In certain embodiments, however,a substrate may not be needed.

An electrochemical cell described herein ma include a separator.Generally, a separator is interposed between a cathode and an anode inan electrochemical cell. The separator may separate or insulates theanode and the cathode from each other preventing short circuiting, andpermit the transport of ions between the anode and the cathode. Theseparator may be porous, wherein the pores may be partially orsubstantially filled with electrolyte. Separators may be supplied asporous free standing films which are interleaved with the anodes and thecathodes during the fabrication of cells. Alternatively, the porousseparator layer may be applied directly to the surface of one of theelectrodes.

Accordingly, in certain embodiments, an electrolyte layer may include asolid portion (e.g., a solid porous network such as a solid electrolyteand/or a separator) and a liquid portion and/or gel portion as describedherein. The pores of the solid portion of the electrolyte layer may havean average size of, for example, greater than 0.01 microns, greater than0.05 microns, greater than 0.1 microns, greater than 0.5 microns,greater than 1 micron, greater than 2 microns, or greater than 5microns. In some cases, the pores of the solid portion of theelectrolyte layer may have an average size of, for example, less than 5microns, less than 3 microns, less than 2 microns, less than 1 micron,less than 0.5 microns, less than 0.1 microns, less than 0.05 microns, orless than 0.1 microns. Other sizes are also possible. Combinations ofthe above-noted ranges are also possible.

In some embodiments, the porosity of separator can be, for example, atleast 30%, at least 40%, at least 50%, at least 60%, at least 70%, atleast 80%, or at least 90%. In certain embodiments, the porosity is lessthan 90%, less than 80%, less than 70%, less than 60%, less than 50%,less than 40%, or less than 30%. Other sizes are also possible.Combinations of the above-noted ranges are also possible.

Separators may be supplied as porous free standing films which areinterleaved with the anodes and the cathodes during the fabrication ofcells. Alternatively, the porous separator layer may be applied directlyto the surface of one of the electrodes, for example, as described inPCT Publication No. WO 99/33125 to Carlson et al. and in U.S. Pat. No.5,194,341 to Bagley et al.

A variety of separator materials are known in the art. Examples ofsuitable solid porous separator materials include, but are not limitedto, polyolefins, such as, for example, polyethylenes (e.g., SETELA™ madeby Tonen Chemical Corp) and polypropylenes, glass fiber filter papers,and ceramic materials. For example, in some embodiments, the separatorcomprises a microporous polyethylene film. Further examples ofseparators and separator materials suitable for use in this inventionare those comprising a microporous xerogel layer, for example, amicroporous pseudo-boehmite layer, which may be provided either as afree standing film or by a direct coating application on one of theelectrodes, as described in U.S. Pat. Nos. 6,153,337 and 6,306,545 byCarlson et al. of the common assignee. Solid electrolytes and gelelectrolytes may also function as a separator in addition to theirelectrolyte function.

In some embodiments, the separator can comprise synthetic ornon-synthetic organic polymeric materials, and can be selected frompolymer/ceramic material hybrid systems such as polymer non-wovenmaterials coated with a ceramic material. Suitable materials for theseparator are polyolefins (e.g., polyethylene or polypropylene) andfluorinated (co)polymers. The separator can comprise a microporous film,in some cases.

The following examples are intended to illustrate certain embodiments ofthe present invention, but do not exemplify the full scope of theinvention.

Example 1

This Example describes the fabrication of a protective structureincluding a composite of inorganic material (ceramic) and polymerportions.

A shadow mask was first positioned on a substrate. Electron beamevaporation was then used to deposit a 0.5 μm-thick layer of anoxysulfide ceramic on the substrate. The shadow mask was removed,leaving a pattern of ceramic islands separated by voids or trenches.FIGS. 8A and 8B show images of ceramic patterns on a substrate. In theimages, the lighter regions 200 are the ceramic islands, and the darkerregions 205 are the voids between the islands. The ceramic islands werealso characterized using Energy Dispersive Spectroscopy (EDS). FIG. 9Ashows another image of the ceramic pattern of FIG. 8A, and FIG. 9B showsan EDS mapping of the ceramic pattern.

A spin coater was used to coat the top surfaces of the ceramic islandswith a silicon oil. The silicon oil acted as a de-wetting agent thatprevented a polymer from adhering to the top surfaces of the ceramicislands. A spin coater was then used to fill the voids in the ceramicpattern with a 0.5 μm-thick layer of a polymer (Oppanol B15, anpolyisobutene). The polymer was then dried. FIGS. 10A-10B show images ofthe ceramic-polymer composite structure, with ceramic portions 200 andpolymeric portions 215.

Due to the presence of the silicon oil de-wetting agent, the polymer didnot adhere to the top surfaces of the ceramic islands. To demonstratethat the polymer coating was not present on the top surfaces of theceramic islands, the polymer-ceramic structure was exposed to liquidnitrogen, which caused the ceramic portions of the structure tofracture. EDS was used to show that the polymer was located within voidsbetween the ceramic islands.

Following spin coating of the polymer into the voids and drying of thepolymer, the polymer-ceramic structure was plasma treated to remove anysilicon oil residue on the exposed ceramic surfaces. The polymer-ceramicstructure was then ready to be coated with lithium metal or with anotherprotective layer (e.g., another ceramic-polymer structure). Theprotective structure (along with lithium metal, if present) can then bereleased from the substrate.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe scope of the present invention.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

The invention claimed is:
 1. An electrode for an electrochemical cell,comprising: a base layer comprising an active electrode species; and aprotective structure positioned to protect the electrode from anelectrolyte when the electrode is arranged in the electrochemical cell,the protective structure having a first side facing the active electrodespecies, and a second side arranged to face the electrolyte, wherein theprotective structure comprises: at least a first and second compositelayer, each layer comprising: a polymer matrix having a plurality ofcavities; and a ceramic material filling at least two cavities of theplurality of cavities; and a continuous ceramic material layerpositioned between the first and second composite layers, wherein eachceramic-filled cavity is in ionic communication with the base layer,wherein the protective structure has an average ionic conductivity of atleast 10⁻⁷ S/cm, and wherein the cavities in the second composite layerare aligned with the cavities in the first composite layer.
 2. Theelectrode of claim 1, wherein the protective structure is impervious tothe electrolyte.
 3. The electrode of claim 1, wherein the plurality ofcavities are arranged in a patterned array within the matrix.
 4. Theelectrode of claim 1, wherein a gel layer is positioned adjacent theprotective structure on a side opposite the base layer.
 5. The electrodeof claim 1, wherein the electrode comprises at least a third compositelayer comprising a polymer matrix having a plurality of cavities and aceramic material filling at least two cavities of the plurality ofcavities.
 6. The electrode of claim 1, wherein the weight of the polymerin the protective structure is at least 2% of the total weight of theprotective structure.
 7. The electrode of claim 1, wherein a ratio ofthe sum of the surface areas of the ceramic-filled cavities to thesurface area of the electrode is at least 0.3.
 8. The electrode of claim1, wherein the electrode is an anode.
 9. The electrode of claim 1,wherein the active electrode species comprises lithium.
 10. Theelectrode of claim 1, wherein the polymer matrix is non-ionicallyconductive.
 11. The electrode of claim 1, wherein the ceramic materialis conductive to lithium ions.
 12. The electrode of claim 1, wherein theceramic material is selected from the group consisting of Li₂O, Li₃N,Al₂O₃, ZrO₂, SiO₂, CeO₂, Al₂TiO₅, oxy-sulfide glass, and combinationsthereof.
 13. The electrode of claim 1, wherein the protective structurehas a thickness of at least 500 nm.
 14. The electrode of claim 1,wherein the elastic modulus of the polymer matrix is at least 2 timessmaller than the elastic modulus of the ceramic material.
 15. Theelectrode of claim 1, wherein each cavity of the plurality of cavitiesis filled with the same material.
 16. The electrode of claim 1, whereinan average largest cross-sectional dimension of the plurality ofcavities is less than or equal to 10 microns.
 17. The electrode of claim1, wherein an average cross-sectional dimension of the plurality ofcavities is greater than or equal to 5 nm.
 18. An electrode for anelectrochemical cell, comprising: a base layer comprising an activeelectrode species; and a protective structure including: at least afirst composite layer and a second composite layer, each comprising apatterned array of cavities within a matrix, wherein a polymer or aceramic material forms the matrix, and the other of the polymer and theceramic material fills at least a portion of the cavities; and acontinuous ceramic material layer positioned between the first andsecond composite layers, wherein the protective structure has an averageionic conductivity of at least 10⁻⁷ S/cm, wherein the cavities in thesecond composite layer are aligned with the cavities in the firstcomposite layer, and wherein the protective structure is positioned toprotect the electrode from an electrolyte when the electrode is arrangedin the electrochemical cell.
 19. The electrode of claim 18, wherein theprotective structure is impervious to the electrolyte.
 20. A method offabricating a protected electrode, the method comprising: forming a baselayer comprising an active electrode species attached to a protectivestructure, wherein the protective structure is formed by: positioning ona substrate at least one layer comprising a first matrix, the firstmatrix comprising a first polymer or a first ceramic material, and thefirst matrix comprising a patterned array of cavities; filling at leasta portion of the cavities in the first matrix with the other of thefirst polymer and the first ceramic material to form a first compositelayer; positioning a continuous ceramic material layer on the firstlayer of the matrix; positioning on the continuous ceramic materiallayer at least a second layer comprising a second matrix, the secondmatrix comprising a second polymer or a second ceramic material, and thesecond matrix comprising a patterned array of cavities; filling at leasta portion of the cavities in the second matrix with the other of thesecond polymer and the second ceramic material to form a secondcomposite layer, wherein the composite layer has an average ionicconductivity of at least 10⁻⁷ S/cm, wherein the cavities in the secondcomposite layer are aligned with the cavities in the first compositelayer, and wherein the protective structure is positioned to protect theelectrode from an electrolyte when the electrode is arranged in anelectrochemical cell.
 21. The method of claim 20, wherein the compositelayer is impervious to the electrolyte.